本文關(guān)鍵詞：應(yīng)用基于GPU的離散單元法模擬研究立管顆粒流動　出處：《中國科學院大學(中國科學院過程工程研究所)》2017年博士論文　論文類型：學位論文

  更多相關(guān)文章： 離散單元法(DEM) 立管排料穩(wěn)定性 特征區(qū)域 關(guān)鍵轉(zhuǎn)變區(qū)域 臨界料柱高度 當量重力理論模型

【摘要】：立管系統(tǒng)憑借其構(gòu)造簡單、造價低廉等優(yōu)點,廣泛應(yīng)用于顆粒物料的輸送。但實際工業(yè)應(yīng)用立管仍然面臨著不穩(wěn)定排料這一挑戰(zhàn),不穩(wěn)定排料不僅降低了顆粒的輸送效率,而且影響著生產(chǎn)運行的穩(wěn)定性和安全性。已有研究工作雖然對立管不穩(wěn)定排料有一定研究,但其本質(zhì)原因仍不清楚。本論文從立管內(nèi)顆粒流動入手,在闡述清楚顆粒流動機理的基礎(chǔ)上,揭示了立管排料穩(wěn)定性問題的本質(zhì);同時,構(gòu)建了立管穩(wěn)定運行的約束性方程;并拓展了當量重力理論模型用于模擬負壓差下的立管排料。理解立管排料穩(wěn)定性的關(guān)鍵是明確立管內(nèi)顆粒流動特征及機理。傳統(tǒng)的立管排料模擬研究中,料面高度普遍偏低,不足以擺脫孔口對其上部顆粒的影響,導致立管內(nèi)過渡區(qū)的流動特征及機理不明確。基于此,本論文通過優(yōu)化的離散單元法(DEM),通過提高模擬料面高度,完全擺脫了孔口的影響,明確了過渡區(qū)的流動特征及機理。結(jié)果表明,在立管排料狀態(tài)改變過程中,過渡區(qū)內(nèi)存在關(guān)鍵轉(zhuǎn)變區(qū)域。當關(guān)鍵轉(zhuǎn)變區(qū)域出現(xiàn)不穩(wěn)定流動后,加速顆粒傳遞到孔口處需要一定時間,在這段時間,孔口處顆粒速度并無變化,立管依然維持穩(wěn)定排料。這也揭示了立管排料穩(wěn)定性問題的本質(zhì)其實是立管內(nèi)顆粒流動穩(wěn)定性發(fā)生了變化,維持顆粒分布平衡的借以克服重力的顆粒與管壁面之間穩(wěn)定摩擦作用消失,排料量的波動只是顆粒流動變化的作用結(jié)果,也是立管內(nèi)不穩(wěn)定流動的宏觀表現(xiàn)。在此基礎(chǔ)上,將關(guān)鍵轉(zhuǎn)變區(qū)域空隙率初始變化時所對應(yīng)的立管料面高度定義為避免不穩(wěn)定流動的臨界料柱高度。在深入研究了顆粒性質(zhì)(如顆粒密度、顆粒內(nèi)摩擦系數(shù))以及設(shè)備設(shè)計參數(shù)(孔口尺寸)對立管臨界料柱高度的基礎(chǔ)上,構(gòu)建了立管穩(wěn)定運行的約束性方程,為相關(guān)工業(yè)設(shè)計及操控提供了理論指導。另外,傳統(tǒng)負壓差立管排料模擬采用CFD-DEM耦合的方法,計算過程復(fù)雜。針對該問題,本文結(jié)合散料力學和DEM模型,提出了當量重力理論模型,用以計算負壓差情況下的立管排料。該模型通過散料力學理論優(yōu)化DEM模型中的重力加速度項,無需DEM和其它流體軟件進行耦合,達到了簡化模型和提升效率的效果,為后續(xù)展開立管研究奠定了基礎(chǔ)。
[Abstract]:Riser system with its simple structure, low cost and other advantages, is widely used in conveying granular materials. But the actual industrial application of riser is still faced with unstable discharge this challenge, unstable discharge not only reduces the transmission efficiency of the particles, but also affects the stability and safety of the operation. The existing research work although the riser unstable discharge has some research, but its essence is still not clear. In this thesis, the vertical pipe flow of particles, in this clear basic particle flow mechanism, reveals the essence of riser discharge stability; at the same time, the construction of the riser constraint equation and stable operation; expand the equivalent theory of gravity model for the simulation of the standpipe discharge. The discharge stability of vertical pipe understanding key is clear vertical flow characteristics and mechanism of tube particles. The traditional riser discharge simulation study, the burden The height is generally low, not enough to get rid of the upper orifice particles, the flow characteristics and mechanism of vertical transition zone inside the tube is not clear. Based on this, this paper through the optimization of the discrete element method (DEM), by increasing the simulation burden height, completely out of the hole influence, clear flow characteristics and mechanism the transition zone. The results showed that in the riser discharge state change process, there is the key transition region of the transition zone. When the key transition region of unstable flow, accelerate the particles transfer to the orifice will take some time, during this time, the orifice particle velocity does not change, still maintain a stable discharge tube. It also reveals the riser nature of discharging stability problem is in fact a vertical pipe flow stability of particles changed, maintain a balance in order to overcome the particle distribution of gravity and particle wall steady friction dissipation Yet, the discharge quantity of particle flow volatility is the change of the results, the macro performance is vertical unstable flow tube. On this basis, the riser material height is defined as the critical to avoid the unstable flow column height corresponding to the key transition region when the change of initial void ratio. In depth study of the particles properties (such as particle density, particle friction coefficient) and design parameters of equipment (Kong Kou size) riser critical material column height on the basis of the construction of the riser constraint equation of stable operation, providing theoretical guidance for industrial design and control. In addition, the traditional standpipe method is used to simulate the discharge CFD-DEM coupling, complex calculation process. Aiming at this problem, the bulk material mechanics and the DEM model this paper proposed equivalent theory of gravity model, calculating the standpipe discharge conditions for the model. Through the material mechanics The optimization of gravity acceleration in DEM model does not require coupling of DEM and other fluid software. It achieves the effect of simplifying model and improving efficiency, and lays the foundation for further research on riser.

【學位授予單位】：中國科學院大學(中國科學院過程工程研究所)
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TQ022

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